Curium

Curium

Curium is a transuranic radioactive chemical element with the symbol Cm and atomic number 96. This element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie - both were known for their research on radioactivity. Curium was first intentionally produced and identified in July 1944 by the group of Glenn T. Seaborg at the University of California, Berkeley. The discovery was kept secret and only released to the public in November 1945. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 20 grams of curium.

Curium is a hard, dense, silvery metal with a relatively high melting point and boiling point for an actinide. Whereas it is paramagnetic at ambient conditions, it becomes antiferromagnetic upon cooling, and other magnetic transitions are also observed for many curium compounds. In compounds, curium usually exhibits valence +3 and sometimes +4, and the +3 valence is predominant in solutions. Curium readily oxidizes, and its oxides are a dominant form of this element. It forms strongly fluorescent complexes with various organic compounds, but there is no evidence of its incorporation into bacteria and archaea. When introduced into the human body, curium accumulates in the bones, lungs and liver, where it promotes cancer.

All known isotopes of curium are radioactive and have a small critical mass for a sustained nuclear chain reaction. They predominantly emit α-particles, and the heat released in this process can potentially produce electricity in radioisotope thermoelectric generators. This application is hindered by the scarcity, high cost and radioactivity of curium isotopes. Curium is used in production of heavier actinides and of the 238Pu radionuclide for power sources in artificial pacemakers. It served as the α-source in the alpha particle X-ray spectrometers installed on the Sojourner, Mars, Mars 96, Athena, Spirit and Opportunity rovers as well as the Mars Science Laboratory to analyze the composition and structure of the rocks on the surface of Mars and the Moon. Such a spectrometer will also be used by the Philae lander of the Rosetta spacecraft to probe the surface of the 67P/Churyumov-Gerasimenko comet.

Occurrence


The longest-lived isotope of curium, 247Cm, has a half-life of 15.6 million years. Therefore, all primordial curium, that is curium present on the Earth during its formation, should have decayed by now. Curium is produced artificially, in small quantities for research purposes. Furthermore, it occurs in spent nuclear fuel. Curium is present in nature in certain areas used for the atmospheric nuclear weapons tests, which were conducted between 1945 and 1980. So the analysis of the debris at the testing site of the first U.S. hydrogen bomb, Ivy Mike, (1 November 1952, Enewetak Atoll), beside einsteinium, fermium, plutonium and americium also revealed isotopes of berkelium, californium and curium, in particular 245Cm, 246Cm and smaller quantities of 247Cm, 248Cm and 249Cm. For reasons of military secrecy, this result was published only in 1956.

Atmospheric curium compounds are poorly soluble in common solvents and mostly adhere to soil particles. Soil analysis revealed about 4,000 times higher concentration of curium at the sandy soil particles than in water present in the soil pores. An even higher ratio of about 18,000 was measured in loam soils.

A few atoms of curium can be produced by neutron capture reactions and beta decay in very highly concentrated uranium-bearing deposits.

Symbol		Cm
Atomic Number		96
Atomic Weight		247.0703
Oxidation States		+3
Electronegativity, Pauling		1.3
State at RT		Solid, Metal
Melting Point, K
Boiling Point, K

Appearance and Characteristics of Curium

Harmful effects:

Curium is harmful due to its radioactivity. It accumulates in bones and destroys the marrow, stopping the formation of red blood cells.

Characteristics:

• Curium is a hard, dense radioactive silvery-white metal.
• It tarnishes slowly in dry air at room temperature.
• Most compounds of trivalent curium are slightly yellow in color.
• Curium is highly radioactive and it glows red in the dark. 

Uses of Curium

• Curium is mainly used for scientific research purposes.
• Curium-244 was used in the Alpha Proton X-ray Spectrometer (APXS) which measured the abundance of chemical elements in rocks and soils on Mars.
• Curium-244 is a strong alpha emitter and is being studied as a potential power source in radioisotope thermoelectric generators (RTGs) for use in spacecraft and other remote applications.

Transuranium elements discovery and experiments. 1963 chemistry educational documentary narrated by Glenn Seaborg, Stanley Thompson and Albert Ghiorso.